In regard to the surface light emitting type semiconductor laser, since a laser beam is outputted from the surface of laminated semiconductor layers in the vertical direction, it is not necessary to mount a laser chip laterally, and it is easily and precisely positioned. These make it convenient to use. As a conventional surface light emitting type semiconductor laser, the structure shown in FIG. 5 is well known. More specifically, on a semiconductor substrate 41 formed of GaAs, for example, there is formed a lower multilayer reflection film 42 called DBR (Distributed Brag Reflector) having a structure in which semiconductor layers having different refractive indexes are laminated so as to reflect the light having a specific frequency band. Then, there are formed thereon a light emitting layer forming portion 46 comprising a lower spacer layer, an active layer and an upper spacer layer which are not shown, and an upper multilayer reflection film 48 comprising the DBR. Then, an insulating region 47 is formed by implanting ion such as proton to a part except for a current injection region A serving as an emission region. Upper and lower electrodes which are not shown are provided on the front surface of laminated semiconductor layers and the back surface of the semiconductor substrate so that the laser beam is outputted from a not-shown small outlet which is formed on the upper electrode and about several μm in diameter, through the upper multilayer reflection film 48 whose reflection factor is made to be a little smaller than the lower multilayer reflection film 42.
In addition, as shown in FIG. 6, instead of insulating a part of semiconductor layers by ion implantation using proton, recently there has been proposed a semiconductor laser having a structure in which a semiconductor layer to be selectively oxidized which comprises AlAs or the like and is likely to be oxidized by water vapor or the like is intervened between the light emitting layer forming portion 46 and the upper multilayer reflection film 48, its outer peripheral part is etched away such that the current injection region and a certain region of its outer periphery are left in the shape of mesa and then, oxidation treatment is performed such that the semiconductor layer is selectively oxidized from the exposed peripheral part under the atmosphere of water vapor but the current injection region A is not oxidized to form a current limiting layer 49. Thus, the current injection region A can be formed within a desired range.
Either of the above described semiconductor laser has a structure in which the current injection region and the outlet of the laser beam are formed in the center of the chip from a viewpoint of symmetry in manufacturing a product. Meanwhile, in this kind of surface light emitting type semiconductor laser as well as an end face emission type semiconductor laser, it is necessary to automatically control the amount of emitting light by monitoring the output of the semiconductor laser such that it is constant when it is used as the light source of the pickup or the like. However, since the lower multilayer reflection film 42 in the surface light emitting type semiconductor laser described above is formed to have high reflection factor of 99.9% or more and the light scarcely comes out of the back surface of the semiconductor substrate 41, the amount of emitting light cannot be monitored by the output from the opposite side of emission surface, that is, the back surface, which is unlike in the end face emission type semiconductor laser. Therefore, as shown in FIG. 7, the following has been attempted, that is, a surface light emitting type semiconductor laser chip 12 is mounted on a light receiving element 13 and the reflected light from a transparent body 26 provided in a transmission window of a cap (not shown) is detected and monitored by the light receiving element 13.
As described above, when the surface light emitting type semiconductor laser is used as the light source of the pickup or the like, since the light coming out of the opposite side of the emitting surface can be hardly used in monitoring the amount of emitting light, it has been thought that some light reflected from the transparent body in the transmission window is used for monitoring the light. However, the reflected light from the transparent body is very scarce such as approximately 10%, the size of the surface light emitting type semiconductor laser chip is 200 μm to 300 μm square and the outlet 10a of the laser beam is several μm or so in a diameter. Thus, when the distance L between the surface of the laser chip 12 and the transparent body 26 is decreased, the area of the reflected light (projected area) in the light receiving element surface becomes very small. When a divergent angle ω (referring to FIG. 7) of the laser beam is around 16° and the distance L is 1 mm or less, the projected area is almost the same size as the laser chip. In this case, the reflected light from the transparent body 26 mostly returns to the surface of the laser chip 12 without being detected by the light receiving element 13 and consequently the reflected light cannot be precisely monitored.